Required Practical 7 Flashcards
Use of chromatography to investigate the pigments isolated from leaves of different plants, eg, leaves from shade-tolerant and shade-intolerant plants or leaves of different colours.
1
Q
Describe how pigments from a leaf of a plant can be isolated with paper chromatography.
A
- Crush leaves with solvent to extract pigments.
- Draw a pencil line on filter/chromatography paper, 1 cm above bottom.
- Add a drop of extract to line (point of origin).
- Stand paper in boiling tube of (organic) solvent below point of origin.
- Add lid and leave to run (solvent moves up, carrying dissolved pigments).
- Remove before solvent reaches top and mark solvent front with pencil.
2
Q
Explain why the origin should be drawn in pencil rather than ink.
A
- Ink is soluble in solvent.
- So ink would mix with pigments / line would move.
3
Q
Explain why the point of origin should be above the level of the solvent.
A
- Pigments are soluble in solvent.
- So would run off paper / spots dissolve into solvent.
4
Q
Explain why a pigment may not move up the chromatography paper in one solvent.
A
- May be soluble in one solvent but insoluble in another.
5
Q
Describe how pigments can be identified.
A
- Rf value = distance moved by spot / distance moved by solvent front.
- Compare Rf value to published value.
6
Q
Explain why the solvent front should be marked once chromatography paper is removed.
A
- Once solvent evaporates, solvent front not visible.
7
Q
Explain why the centre of each pigment spot should be measured.
A
- Standardises readings as pigment is spread out.
- So allows comparisons to be made.
8
Q
Explain why the obtained Rf values were similar, but not identical, to the published values.
A
- Different solvent / paper / running conditions may affect Rf value.
9
Q
Explain why Rf values are used and not the distances moved by pigment spots.
A
- Solvent / pigment moves different distances.
- Rf value is constant for same pigment / can be compared.
